Protein kinases (PKs) are a group of enzymes that regulate diverse, important biological processes including cell growth, survival and differentiation, organ formation and morphogenesis, neovascularization, tissue repair and regeneration, among others. Protein kinases exert their physiological functions through catalyzing the phosphorylation of proteins (or substrates) and thereby modulating the cellular activities of the substrates in various biological contexts. In addition to the functions in normal tissues/organs, many protein kinases also play more specialized roles in a host of human diseases including cancer. A subset of protein kinases (also referred to as oncogenic protein kinases), when dysregulated, can cause tumor formation and growth, and further contribute to tumor maintenance and progression (Blume-Jensen P et al, Nature 2001, 411(6835):355-365). Thus far, oncogenic protein kinases represent one of the largest and most attractive groups of protein targets for cancer intervention and drug development.
c-Met, a proto-oncogene, is a member of a distinct subfamily of heterodimeric receptor tyrosine kinases which include Met, Ron, and Sea (Birchmeier, C. et al., Nat. Rev. Mol. Cell. Biol. 2003, 4(12):915-925; Christensen, J. G. et al., Cancer Lett. 2005, 225(1): 1-26). The only high affinity ligand for c-Met is the hepatocyte growth factor (HGF), also known as scatter factor (SF). Binding of HGF to c-Met induces activation of the receptor via autophosphorylation resulting in an increase of receptor dependent signaling. Both c-Met and HGF are widely expressed in a variety of organs, but their expression is normally confined to the cells of epithelial and mesenchymal origin, respectively. The biological functions of c-Met (or c-Met signaling pathway) in normal tissues and human malignancies such as cancer have been well documented (Christensen, J. G. et al., Cancer Lett. 2005, 225(1):1-26; Corso, S. et al., Trends in Mol. Med. 2005, 11(6):284-292).
HGF and c-Met are each required for normal mammalian development, and abnormalities reported in both HGF- and c-Met-null mice are consistent with proximity of embryonic expression and epithelial-mesenchymal transition defects during organ morphogenesis (Christensen, J. G. et al., Cancer Lett. 2005, 225(1):1-26). Consistent with these findings, the transduction of signaling and subsequent biological effects of HGF/c-Met pathway have been shown to be important for epithelial-mesenchymal interaction and regulation of cell migration, invasion, cell proliferation and survival, angiogenesis, morphogenesis and organization of three-dimensional tubular structures (e.g. renal tubular cells, gland formation) during development. The specific consequences of c-Met pathway activation in a given cell/tissue are highly context-dependent.
Dysregulated c-Met pathway plays important and sometimes causative (in the case of genetic alterations) roles in tumor formation, growth, maintenance and progression (Birchmeier, C. et al., Nat. Rev. Mol. Cell. Biol. 2003, 4(12):915-925; Boccaccio, C. et al., Nat. Rev. Cancer 2006, 6(8):637-645; Christensen, J. G. et al., Cancer Lett. 2005, 225(1): 1-26). HGF and/or c-Met are overexpressed in significant portions of most human cancers, and are often associated with poor clinical outcomes such as more aggressive disease, disease progression, tumor metastasis and shortened patient survival. Further, patients with high levels of HGF/c-Met proteins are more resistant to chemotherapy and radiotherapy. In addition to the abnormal HGF/c-Met expression, the c-Met receptor can also be activated in cancer patients through genetic mutations (both germline and somatic) and gene amplification. Although gene amplification and mutations are the most common genetic alterations that have been reported in patients, the receptor can also be activated by deletions, truncations, gene rearrangement, as well as abnormal receptor processing and defective negative regulatory mechanisms.
The various cancers in which c-Met is implicated include, but are not limited to: carcinomas (e.g., bladder, breast, cervical, cholangiocarcinoma, colorectal, esophageal, gastric, head and neck, kidney, liver, lung, nasopharygeal, ovarian, pancreas, prostate, thyroid); musculoskeletal sarcomas (e.g., osteosarcaoma, synovial sarcoma, rhabdomyosarcoma); soft tissue sarcomas (e.g., MFH/fibrosarcoma, leiomyosarcoma, Kaposi's sarcoma); hematopoietic malignancies (e.g., multiple myeloma, lymphomas, adult T cell leukemia, acute myelogenous leukemia, chronic myeloid leukemia); and other neoplasms (e.g., glioblastomas, astrocytomas, melanoma, mesothelioma and Wilm's tumor (www.vai.org/met/; Christensen, J. G. et al., Cancer Lett. 2005, 225(1):1-26).
The notion that the activated c-Met pathway contributes to tumor formation and progression and could be a good target for effective cancer intervention has been further solidified by numerous preclinical studies (Birchmeier, C. et al., Nat. Rev. Mol. Cell. Biol. 2003, 4(12):915-925; Christensen, J. G. et al., Cancer Lett. 2005, 225(1):1-26; Corso, S. et al., Trends in Mol. Med. 2005, 11(6):284-292). For example, studies showed that the tpr-met fusion gene, overexpression of c-met and activated c-met mutations all caused oncogenic transformation of various model cell lines and resulted in tumor formation and metastasis in mice. More importantly, significant anti-tumor (sometimes tumor regression) and anti-metastasis activities have been demonstrated in vitro and in vivo with agents that specifically impair and/or block HGF/c-Met signaling. Those agents include anti-HGF and anti-c-Met antibodies, HGF peptide antagonists, decoy c-Met receptor, c-Met peptide antagonists, dominant negative c-Met mutations, c-Met specific antisense oligonucleotides and ribozymes, and selective small molecule c-Met kinase inhibitors (Christensen, J. G. et al., Cancer Lett. 2005, 225(1):1-26).
In addition to the established role in cancer, abnormal HGF/c-Met signaling is also implicated in atherosclerosis, lung fibrosis, renal fibrosis and regeneration, liver diseases, allergic disorders, inflammatory and autoimmune disorders, cerebrovascular diseases, cardiovascular diseases, conditions associated with organ transplantation (Ma, H. et al., Atherosclerosis. 2002, 164(1):79-87; Crestani, B. et al., Lab. Invest. 2002, 82(8):1015-1022; Sequra-Flores, A. A. et al., Rev. Gastroenterol. Mex. 2004, 69(4)243-250; Morishita, R. et al., Curr. Gene Ther. 2004, 4(2)199-206; Morishita, R. et al., Endocr. J. 2002, 49(3)273-284; Liu, Y., Curr. Opin. Nephrol. Hypertens. 2002, 11(1):23-30; Matsumoto, K. et al., Kidney Int. 2001, 59(6):2023-2038; Balkovetz, D. F. et al., Int. Rev. Cytol. 1999, 186:225-250; Miyazawa, T. et al., J. Cereb. Blood Flow Metab. 1998, 18(4)345-348; Koch, A. E. et al., Arthritis Rheum. 1996, 39(9):1566-1575; Futamatsu, H. et al., Circ. Res. 2005, 96(8)823-830; Eguchi, S. et al., Clin. Transplant. 1999, 13(6)536-544).
New or improved forms of existing agents which inhibit kinases such as c-Met are continually needed for developing more effective pharmaceuticals to treat cancer and other diseases. The compounds and salts described herein are directed toward these needs and other ends.